1,721,047 research outputs found
Wind tunnel investigation of the wake-flow response for a floating turbine subjected to surge motion
Full text linkFloating wind turbines undergo large translation motions allowed by the high compliancy of the support structure. Large motions affect the rotor aerodynamic response and wake. This paper examines wake measurements of a wind tunnel experiment with a scale model of the DTU 10MW subjected to imposed harmonic surge motion. The effect of surge motion on the wake is detected by means of spectral analysis of velocity data. It is found that when the rotor undergoes surge motion, periodic forcing is introduced into the fluid, which produces a harmonic variation of the wake speed. The velocity perturbation around the rotor is then convected downstream at about the average axial velocity in the wake. The amplitude of the velocity pulsation at 2.3D is radially-dependent, and is correlated to the amplitude of the variation of the normal-force distribution along the blade
Wake measurements of small-scale vertical axis wind turbines at Politecnico di Milano: A critical review
No full textIn the last ten years, four measurement campaigns were performed at Politecnico di Milano on two Darrieus Vertical Axis Wind Turbines (VAWT) for micro-generation of different architecture (H-shaped vs troposkien), but sharing the blade number (3), the blade profile (NACA 0021), and the swept area (1.5 m2). The experiments, carried out in the large-scale wind tunnel of Politecnico di Milano, included detailed wake measurements. This paper presents a review of the research activities related to velocity and turbulence measurements in the wake, proposing an analysis of both the technical aspects and the scientific outcomes of the investigation. In particular, the wakes of these turbines were measured on several surfaces downstream of the rotors for different tip speed ratios and different Reynolds numbers, searching for corresponding conditions between the two rotors. The paper first presents the technical issues involved in measuring the flow velocity in the wake of VAWT rotors with intrusive techniques such as hot wire anemometers and pressure probes. The second part of the paper proposes a comprehensive analysis of the wakes shed by the tested models. The wakes appear asymmetric and roughly follow the shape of the rotor, their width and velocity deficit being strongly dependent on the tip speed ratio. Flow angle measurements show the onset of large-scale tip vortices, for both the H-shape and the troposkien rotors, even though resulting from different aerodynamic mechanisms in the two architectures. A discussion on the impact of the wake features on the implementation of VAWTs in the urban environment concludes the paper
Low intensity warfarin therapy.
No full textBACKGROUND AND OBJECTIVE: Several studies comparing different intensities of oral anticoagulant treatment have clearly shown a relationship between bleeding complications and prolongation of prothrombin time. In the early '50s, de Takats suggested that low-dose oral anticoagulants might be as effective as higher doses in preventing thrombosis, at a lower risk of bleeding. This review article examines the potential of low dose warfarin therapy.
INFORMATION SOURCES: The authors have been working in this field, contributing original papers. In addition, the material examined in this article includes articles published in the journals covered by the Science Citation Index and MedLine.
STATE OF ART AND PERSPECTIVES: The hypothesis that low-dose oral anticoagulants can be effective in preventing thrombosis was first proven by experiments in animal models, and showed that a prothrombin time ratio as low as 1.14 using rabbit brain thromboplastin was still able to confer some inhibition of experimental thrombosis. Low-dose or very low-dose warfarin were subsequently demonstrated to be effective in patients with morbid obesity and decreased antithrombin III functional and antigenic levels, in patients with indwelling catheters, in patients undergoing gynecological surgery, as well as in patients with stage IV breast cancer. Low-dose warfarin is also effective in the prevention of embolic strokes in patients with non-rheumatic atrial fibrillation. However, older patients (> 75 years), who have a very high risk of bleeding, might be safer taking a very low dose of warfarin (i.e., a daily dose of 1-1.25 mg). Moreover, after a period of run-in, a fixed, very low-dose warfarin schedule does not need further laboratory control, which is a factor that could contribute to the full acceptance of treatment by patients and could stimulate a broader prescription of warfarin for the primary prevention of stroke in older patients with nonrheumatic atrial fibrillation. Therefore, we have organized a multicenter clinical trial in which 1000 patients with non-rheumatic atrial fibrillation will be randomized to receive either a fixed mini-dose of warfarin or a standard dose. Positive results might permit the treatment of most older patients with non-rheumatic atrial fibrillation, creating a benefit for the community as a consequence of its effective prevention of disabling strokes.Background and Objective. Several studies comparing different intensities of oral anticoagulant treatment have clearly shown a relationship between bleeding complications and prolongation of prothrombin time. In the early 50s, de Takats suggested that low-dose oral anticoagulants might be as effective as higher doses in preventing thrombosis, at a lower risk of bleeding. This review article examines the potential of low dose warfatin therapy. Information sources. The authors have been working in this field, contributing original papers. In addition, the material examined in this article includes articles published in the journals covered by the Science Citation Index® and MedLine®. State of art and Perspectives. The hypothesis that low-dose oral anticoagulants can be effective in preventing thrombosis was first proven by experiments in animal models, and showed that a prothrombin time ratio as low as 1.14 using rabbit brain thromboplastin was still able to confer some inhibition of experimental thrombosis. Low-dose or very low-dose warfarin were subsequently demonstrated to be effective in patients with morbid obesity and decreased antithrombin III functional and antigenic levels, in patients with indwelling catheters, in patients undergoing gynecological surgery, as well as in patients with stage IV breast cancer. Low-dose warfarin is also effective in the prevention of embolic strokes in patients with non-rheumatic atrial fibrillation. However, older patients (>75 years), who have a very high risk of bleeding, might be safer taking a very low dose of warfarin (i.e., a daily dose of 1-1.25 mg). Moreover, after a period of run-in, a fixed, very low-dose warfarin schedule does not need further laboratory control, which is a factor that could contribute to the full acceptance of treatment by patients and could stimulate a broader prescription of warfarin for the primary prevention of stroke in older patients with non-rheumatic atrial fibrillation. Therefore, we have organized a multicenter clinical trial in which 1000 patients with non-rheumatic atrial fibrillation will be randomized to receive either a fixed mini-dose of warfarin or a standard dose. Positive results might permit the treatment of most older patients with non-rheumatic atrial fibrillation, creating a benefit for the community as consequence of its effective prevention of disabling strokes
REVERSAL OF EXCESSIVE EFFECT OF REGULAR ANTICOAGULATION - LOW ORAL DOSE OF PHYTONADIONE (VITAMIN-K1) COMPARED WITH WARFARIN DISCONTINUATION
No full textTo determine the best way to reverse the excessive effect of regular anticoagulation in patients with INR > 5 and no bleeding complications, 23 patients with INR > 5 were randomly subdivided into two groups: group A (n = 12) discontinued warfarin for one day and group B (n = 11) received 2 mg of vitamin K1 orally in addition to the usual warfarin dose. INR was determined after 24 h (day 1), after which both groups continued with their usual dose of warfarin. After 48 h (day 2), warfarin dosage was changed according to the INR value. On day 9, INR values were determined again. Five out of twelve patients in group A had INR values > 5 on day 1. One patient in group A had an INR value < 5 both on days 1 and 2. All eleven patients in group B had INR values < 5 on day 1, and all but one on day 2. On day 9, INR values were acceptable (INR 2.0-4.5) in ten group A patients and eight group B patients. These findings suggest that a low oral dose of vitamin K1 is a convenient treatment for excessive anticoagulation in patients with no bleeding complications
Modelling of Wind Turbines as Porous Disks for Wind Farm Flow Studies
Full text linkThis study explores the use of porous disks as a modeling approach for wind turbines in both wind tunnel experiments and computational fluid dynamics (CFD) simulations. Experimental testing is conducted on a 0.2m diameter disk made of wired mesh, measuring its wake for several yaw angles. The experiment is recreated in a CFD environment based on the porous-medium approach. The CFD model is validated against part of the measurements and it is used to further investigate the disk wake. Results indicate the porous disk wake resembles that of a wind turbine, especially at a downstream distance of four diameters, and the CFD model effectively captures the disk behavior. Discrepancies between experiment and CFD appear further downstream mainly due to the wake recovery process being only partially captured by the CFD model. When the disk has a yaw angle the wake is displaced laterally, but less than in a widely-accepted deflection model, and this could be due to the lack of wake curling
Experimental assessment of the effects of a porous double skin façade system on cladding loads
Full text linkThe high-efficiency façades, such as porous double skins, have become increasingly popular due to the recent technological progress in architecture. The so-called porous double skin façade (DSF) systems, which are constituted by a permeable layer over a closed inner façade, are often adopted to reduce the system energy demand. However, as expected, the porous skin alters the wind-induced pressures acting on the inner façade. Therefore, the cladding loads for such a façade system has to be accurately estimated performing wind tunnel tests. Using the low-rise buildings of the New Bocconi Campus as a case study, we present the experimental wind tunnel methodologies utilized to assess the wind-induced peak pressures acting on the inner glazed skin of the porous double skin façade system designed for the case at hands. In particular, the reduction of both the positive and negative peak pressures estimated for the inner façade is addressed when comparing the standard façade to the porous DSF case. In addition, the valuable data set of the pressure signals acquired for the porous DSF system studied, allows one to investigate the dependence of the computed peak pressures on the averaging time utilized for the extreme value estimates
Super-long bridges with floating towers: The role of multi-box decks and Hardware-In-the-Loop technology for wind tunnel tests
No full textNonlinear modelling of aerodynamic self-excited forces: An experimental study
Full text linkThe bridge aerodynamics research community is currently discussing several nonlinear wind load models for bridge decks, but no definite conclusion on which model is superior to the others is currently available. In this paper, we use experimental data for a double-deck section model tested in an advanced forced vibration rig to study the observed nonlinearities and to gain insight into what characteristics the nonlinear load model should be capable of modelling. Single harmonic horizontal, vertical and pitching motion; combined motion; and stochastic motion are considered. This approach allows the investigation of a more extensive range of nonlinear behaviours than regular wind tunnel testing. The typical nonlinear characteristics observed are mean drift, deviation from superposition and harmonic distortion. Further, we introduce a simple response-surface model for force prediction using polynomial combinations of the inputs and its derivatives. The model helps to gain further insight into the nonlinearity of the problem at hand and to select which refined modelling approach can be used in future work
Aerodynamic Tailoring of a Bluff Deck Section Subjected to Inclined Winds Due to the Complex Orography of the Construction Site
No full textPeculiar aerodynamic advantages and problems of twin-box girder decks for long span crossings
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